1. Field of the Invention
The present invention relates to a communication support system capable of sending a message to the most suitable user with regard to space (or space and time) even if the sender of the message does not specify the receiver.
2. Description of Related Art
As is generally known, the private paging system and the liaison communication system works are private radio communication systems used in service areas, such as within the premises or in limited regions. Such private radio communication systems are installed on the assumption that people communicate by voice or simple information transfer is carried out from a host station to subordinate stations. PHS (personal handyphone system) is a radio system having a high potential for data transmission. With regard to the private radio system and PHS, there is a detailed description in “Mobile Communications Handbook” (jointly edited by Tadao Saito and Keizo Tachikawa, published by Ohmsha, Nov. 15, 1995), for example.
As a system that utilizes position information in a private branch exchange, there is a plant network system disclosed in Japanese Patent Application No. Hei 8-313837. This system transmits, by using PHS service, data necessary for plant maintenance to places the plant maintenance person move to in advance.
In the roaming of the PHS terminal, because the areas where the PHS terminal moves around can be grasped by the PHS service, the PHS terminal can communicates freely in areas other than the preliminarily registered area. With regard to the roaming methods, a method is revealed in Japanese Patent Application Laid-Open No. Hei 7-322340, for example.
As is well known, message transfer service by a radio system is available with information processing terminals or radio paging portable receivers. In this kind of service, messages are addressed to individuals, and the sender is required to specify the address of the receiver or the number of the radio paging portable receiver when sending a message. With regard to the message transfer method to a radio paging portable receiver, a method is revealed in Japanese Patent Application Laid-Open No. Hei 6-86354, for example.
As mentioned above, in the prior art, it is possible to obtain position information about the user and transfer a message to the user by using a radio system. However, because the sender of a message is required to specify the address of a person as a receiver of the message, it is not always possible to provide message transmission service that can respond to changes in the location or situation of a message receiver.
When there is a message to any user in a given area at a given time, it is more often important to send the message to that area at that time rather than send it to the person.
In a plant operation monitoring system, for example, the plant maintenance person performs periodic inspection in which he/she takes measurements and inspect the equipment in the field. If there are a number of maintenance persons in the plant and a request is issued to check a specific device, an instruction message should preferably be transmitted not to a specific maintenance person but to a maintenance person closest to that device.
Suppose that a message is going to be sent to a person at place B at time A and the request given is that the recipient of the message may be anybody.
In the past, the sender of a message is required to follow a two-step procedure:
Step 1: When time A comes, tracing is performed to find who is at place B.
Step 2: The user at place B is determined, and a message is sent to an address of that user.